The Commons is not the place for the media to be on trial over phone-hacking allegations, the former chairman of the Press Complaints Commission has told followers on Twitter. MPs are too cowardly when it comes to tackling newspapers – and that empowers their editors, Sir Christopher Meyer said.

Meyer, a former British ambassador to Washington who tweets as @SirSocks, tweeted: "The conflicts of interest are so extreme that MPs should be recused from judging the media. But if not the Commons, who? Newspapers and their editors are empowered by the pusillanimity of MPs who attribute to them powers they simply do not have."

Meyer defended the PCC's handling of the phone-hacking allegations. He was chairman of the watchdog during its original investigation into phone hacking by newspapers after the News of the World royal editor, Clive Goodman, and private investigator Glenn Mulcaire were jailed for hacking the phones of royal aides and celebrities. Andy Coulson, now the Conservatives' communications chief, resigned as editor of the paper despite insisting he had no knowledge of the hacking. He was not questioned during the original PCC inquiry.

Meyer had stepped down as chairman by the time the PCC reopened that investigation last year following the Guardian's revelation that the tabloid had since made secret payments of £1m to three victims of the practice.

That report concluded there was no new evidence to suggest that the News of the World executive knew of the practice.

Its conclusions were heavily criticised by MPs on the cross-party parliamentary select committee inquiry into press standards. They described the PCC as toothless and dismissed its findings as simplistic and surprising. The PCC inquiry had not fully or forensically considered all the evidence, said the committee in its 167-page report.

The PCC was criticised at the time for not questioning key executives face to face and for accepting written statements as evidence, including one from the present editor of the News of the World, who was not even at the newspaper at the time of the Goodman hacking.

But, said Meyer on Twitter: "If the PCC had the power to take sworn statements and levy fines, it would be an arm of the state. How many more journos do I have to tell that crime, as in the Regulation of Investigatory Powers Act, is for the police not the PCC?"